FIG. 1 provides a schematic illustration of a fuel system 10 in a diesel engine. The fuel system 10 is shown to include a fuel tank 12, a low pressure fuel pump 14 pumping fuel from the tank 12, a fuel filter 16 that filters the fuel from the pump 14, and a high pressure fuel pump 18 that increases the fuel pressure and feeds the fuel to a fuel reservoir 20. From the fuel reservoir 20, the fuel is distributed to a number of fuel injectors 22 where the fuel is injected and combusted in the engine.
During operation of a diesel engine, air can accumulate within the fuel system, for example within the fuel filter. In addition, air can enter the fuel system as a result of changing the fuel filter. Regardless of how air enters the fuel system, it is desirable to provide means to vent the air from the fuel system because air can interfere with the smooth and continuous delivery of fuel to the engine, decease engine performance and possibly lead to engine damage.
A number of means to vent air from a fuel system have been provided in the past. One such means includes a vent line that connects to the flow line connecting the low pressure pump to the fuel filter, the venting line connecting to the fuel tank so that air is vented into the fuel tank. Another known method is to provide an air vent mechanism on or near the fuel filter. Manually operated mechanical venting valves and venting screws associated with the fuel filter have been often used. These mechanisms can be difficult for a person to actuate, and can lead to fuel spills if they are not actuated properly. To avoid these difficulties, automatic venting has become more common. One automatic venting method is to provide a small orifice in the fuel filter that allows air to flow out of the fuel filter and back to the fuel tank through a vent line.
FIGS. 2A-C illustrate another version of a known automatic venting mechanism 24 associated with a fuel filter. The mechanism 24 is disposed adjacent to, but downstream from, the fuel filter to receive clean fuel via an inlet port 26. A clean fuel exit port 28 leads to the engine and an air vent passage 30 connected to the fuel tank is provided for air venting. A valve mechanism is provided for controlling the flow of air and fuel through the mechanism 24. The valve mechanism includes an inner valve 32 and an outer valve 34 which cooperate together to control the flow.
The valves 32, 34 are actuated by fluid pressure generated by the upstream fuel pump, or in the absence of fuel pump pressure, by gravity. FIG. 2A shows the valves 32, 34 in a position when the engine is turned off, where the valves 32 and 34 are at their lowermost positions with the valve 32 blocking the inlet port 26 and the valve 34 blocking the exit port 28 in an effort to prevent backflow of clean fuel from the exit port 28 back through the inlet port 26. Upon starting of the engine, pressure generated by the fuel pump acts on the lower end of the valve 32, thereby lifting the valve 32 upward as shown in FIG. 2B. In this position, air is able to flow past a gap between the valve 32 and the inside of the valve 34 in which the valve 32 is disposed, through a hole in the top of the valve 34, and out the air vent passage 30 back to the fuel tank. FIG. 2C illustrates the positions of the valves 32, 34 in a topmost position once the air is vented and liquid fuel starts flowing. The fuel acts on the ends of the valves 32, 34 to lift the valves 32, 34 upward. The top of the valve 32 is lifted up to close the hole through the top of the valve 34 and prevent further venting. The valve 34 is lifted upward until a reduced diameter section thereof intersects the exit port 28. Fuel can then flow past the valve 34 between the side of the valve 34 and the interior of the valve housing to the exit port 28.
The mechanism 24 illustrated in FIGS. 2A-C uses two valves 32, 34 that cooperate together in an effort to achieve air venting and prevent backflow of clean fuel. Since two valves are used, the mechanism is somewhat complicated, and the operation of one or both of the valves 32, 34 could be impaired as a result of particulate mater or other contamination accumulating on or in the valves. In addition, the fuel must flow through a relatively narrow opening between the outside of the valve 34 and the interior of the valve housing to reach the exit port 28. This reduces the amount of fuel that can reach the exit port and increases the pressure requirements for the fuel pump for pumping the fuel. Further, an increased differential pressure from filter inlet to outlet will effectively decrease the service interval (i.e. longevity) of the filter.
An improved automatic venting means in a fuel filter system would be beneficial that permits automatic venting and prevents drainback of clean liquid fuel.